Fuch Polishing Using DC Motor: Help Needed

JackMan · 01-01-2008, 01:00 PM

Gents

I think someone has already done this, but I can't find the thread. (Speak up if you have.)

I'm in the midst of redoing my Fuchs, then another set, and I owe a buddy a favor, so I'm going to redue his. (Thanks but I have enough buddies.)

I want to take the pictured DC motor, rescued years ago from a broken tread mill and put on the shelf because I might need it someday, and mount it on my bench and then mount wheels on the motor, turn them to sand and polish.

I need something to adapt the AC 120 power from the house to the motor and some device to then vary the speed.

I have no idea what I"m looking for here, ideas?

Also, anyone have some ideas on how to mount the wheel?

Thanks

Wellborn

Danny_Ocean · 01-01-2008, 01:17 PM

I think it's going to be more trouble than it's worth to try and rig/adapt that motor. Do you have a Northern or Grizzly tools near you? They sell low-to-mid grade quality commercial buffers for less than $400.

But, if you insist, the best way would be to set-up a belt drive system with reducing pulley's. That way you can adjust the speed by changing the pulley size and not have to worry about finding the proper motor controller:

JackMan · 01-01-2008, 02:50 PM

Danny Ocean,

Thanks and I think you're right on the money. Just buy the tool I need, but...

Yes, I could just spend money. But that defeats the purpose. The challenge is putting together a Rub Goldberg assortment of parts to achieve the goal.....

Anyone else?

ZOA NOM · ZOA NOM's Garage

Try this:

kplackmeyer · 01-01-2008, 03:48 PM

I see an AC power cord lying on your bench next to the motor...did you try and plug that sucker directly into AC service? If not, you are going to need an AC to DC transformer, which can get pretty pricy, along with a DC motor controller, which usually can be bought as a single unit:
http://www.clarkerewinds.ie/dc.htm
Don't suppose you have the rest of the treadmill still? It would have had this in it.

If you did plug it directly into the wall, I would reconsider Danny Ocean's suggestion.

Zeke · 01-01-2008, 04:42 PM

I have a lot of tools being a contractor, a woodworker and a metalworker. I wouldn't bother with that. PITA, sorry. But if you take the money and spend it on something appropriate, I think you will come out ahead in the long run.

PS: I have 3 beach grinders and they all do a dedicated task. I don't think any of them were purchased new. Most likely garage sale or similar. They just don't die.

JackMan · 01-01-2008, 05:31 PM

Ok, Milt speaks. Time to go to the pocket book and spend some dough.

I'm going to go price some bench grinders, maybe even a lathe of some sorts....

rick-l · 01-01-2008, 07:51 PM

See if anyone agrees with this analysis for a permanent magnet motor. What I remember....

From the nameplate

hp=2 = 1500 Watts
- @ 3350 torque = 3.14 ft-lbs
- 0.174 ft-lbs/amp
V*I = 2340 Watts so 840 is wasted in the series resistance
The series resistance is 2.59 ohms (P / I^2 or 840 / 18^2)

At nameplate conditions

Vres = 46.67
Vmot = 83.33
k = 0.0248 volts/rpm
L is unknown (and has some influence)

With no mechanical load, no friction; a half wave rectified line voltage would be 161 / pi or 51 volts average so the speed would be 51/.0248 or 2060 rpm

Full wave rectified line voltage (4 diodes) would be 161*2 / pi or 102 volts average so the speed would be 51/.0248 or 4120 rpm

[That 15 amps is the startup current]

JackMan · 01-02-2008, 04:39 AM

Rick

Thanks for the analysis but HUH?

That's greek to me. Just tell me what to do, how to build it??

OMG, you're smart.

wj

Porsche_monkey · 01-02-2008, 05:38 AM

Buy a variac and a bridge rectifier, or just go to an electrical supply house and buy the cheapest dc motor control they sell.

billybek · billybek's Garage

Watch out for two horsepower though. That's enough to rip your arm off and beat you with the bloody end!!

Tim Hancock · 01-02-2008, 06:42 AM

If I were you, I would use some variation of Zoanas's idea above. You are not going to be able to easily come up with a way to solidly mount a wheel to anything unless you have some serious equipment to build a hub. Maybe if you have an old Porsche hub/spindle, you could do it, but it sounds like you may not have any serious fab equipment available to you.

You could buy a cheap hand drill from Harbor Freight and cob up some kind of cradle for it out of wood then simply lower the car onto it (just enough weight to drive the tire/wheel with friction) to drive the tire/wheel on the car like Zoanas shows above. It looks like he simply used a rubber sanding drum holder that can be purchased at Harbor Freight for cheap also. The beauty of the cheap drill is that it will be variable speed and can be had for dirt cheap. The bearings in it wont like the side loading, but it should last plenty long enough do to a bunch of wheels.

dad911 · 01-02-2008, 06:59 AM

Years ago I blocked/braced up the back of a 944, and let the car idle in gear to spin the back wheel.

ZOA NOM · ZOA NOM's Garage

Quote:

Originally Posted by Tim Hancock

If I were you, I would use some variation of Zoanas's idea above. You are not going to be able to easily come up with a way to solidly mount a wheel to anything unless you have some serious equipment to build a hub. Maybe if you have an old Porsche hub/spindle, you could do it, but it sounds like you may not have any serious fab equipment available to you.

You could buy a cheap hand drill from Harbor Freight and cob up some kind of cradle for it out of wood then simply lower the car onto it (just enough weight to drive the tire/wheel with friction) to drive the tire/wheel on the car like Zoanas shows above. It looks like he simply used a rubber sanding drum holder that can be purchased at Harbor Freight for cheap also. The beauty of the cheap drill is that it will be variable speed and can be had for dirt cheap. The bearings in it wont like the side loading, but it should last plenty long enough do to a bunch of wheels.

Yep, and the wheel spun plenty fast. I only needed one hand free to hold the sanding material. I put the drill on it's back, supported by the adjustable handle on the ground. It tilted just enough to apply the friction to the bottom edge of the wheel. Worked like a charm.

You could even fab a heavy base for your DC motor, set it on the floor and run a pulley with a large belt around the wheel.

stevemfr · 01-02-2008, 10:34 AM

I dig the flops, Zoanas

Porsche_monkey · 01-02-2008, 10:36 AM

I don't bother reading his posts. They're secondary.

billybek · billybek's Garage

Strangely hypnotic....

safe · safe's Garage

I used an AC motor and a frequency transformer.
With the transformer you can alter the frequency, in my case to 25hz which in Europe makes a motor turn at half speed.
I got the transformer used for about $100, it could easily be sold for that again.

AUS911SC · 01-02-2008, 12:22 PM

If you want to do your rims properly dont forget to clear reanodise them or they will be back to chipped and scratched condition very quickly. You just have to breathe on the rim and they will mark. This means you will have to use caustic soda (oven cleaner works) or get them professionally dipped to remove the old anodizing, I cant stress this enough. If you are going to paint them in black as per original may I suggest using VHT Satin Black Polyurethane paint as it looks fantastic and is very strong (chip resitant) however dont polish paint for 3 month - you can drive with them though.

Porsche_monkey · 01-02-2008, 12:29 PM

Quote:

Originally Posted by safe

I used an AC motor and a frequency transformer.
With the transformer you can alter the frequency, in my case to 25hz which in Europe makes a motor turn at half speed.
I got the transformer used for about $100, it could easily be sold for that again.

That would be called a VFD here, variable frequency drive. And they are quite cheap now.